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Question 3.93: If we assume a 100-gram sample of fertilizer, then the 30: 1......

If we assume a 100-gram sample of fertilizer, then the 30: 10: 10 percentages become the masses, in grams, of N, \text{P}_2\text{O}_5,\text{ and K}_2\text{O}. These masses may be changed to moles of substance, and then to moles of each element. To get the desired x:y: 1.0 ratio, divide the moles of each element by the moles of potassium.

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A 100-gram sampl e of 30:10:10 fertilizer contains 30\text{ g N, 10 g P}_2\text{O}_5,\text{ and 10 g K}_2\text{O}.

\begin{matrix}\text{Moles N}=(30\text{ g N})\left\lgroup\frac{1\text{ mol N}}{14.01\text{ g N}} \right\rgroup =2.1413\text{ mol N (unrounded)} \end{matrix} \\ \begin{matrix} \text{Moles P}=(10\text{ g P}_2\text{O}_5) \left\lgroup\frac{1\text{ mol P}_2\text{O}_5}{141.94\text{ g P}_2\text{O}_5} \right\rgroup \left\lgroup\frac{2\text{ mol P}}{1\text{ mol P}_2\text{O}_5} \right\rgroup =0.14090\text{ mol P (unrounded)} \end{matrix} \\ \begin{matrix} \text{Moles K}=(10\text{ g K}_2\text{O}) \left\lgroup\frac{1\text{ mol K}_2\text{O}}{94.20\text{ g K}_2\text{O}} \right\rgroup \left\lgroup\frac{2\text{ mol K}}{1\text{ mol K}_2\text{O}} \right\rgroup =0.21231\text{ mol K (unrounded)} \end{matrix}

This gives a ratio of 2.1413:0.14090:0.21231
The ratio must be divided by the moles of K and rounded.
(2.1413/0.21231):(0.14090/0.21231):(0.21231/0.21231)
10.086: 0.66365: 1.000
10:0.66: 1.0

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